Electro-hydraulic drive system

ABSTRACT

Provided is an electro-hydraulic drive system including first and second electro-hydraulic transmissions for driving respective wheels, the transmissions each including an electric motor, a hydraulic pump driven by the electric motor, and a hydraulic motor drive by the hydraulic pump. When used in a turf vehicle, such as a zero-turn-radius mower, the electro-hydraulic drive system operates the wheels independently from an engine of the mower, thereby allowing the mower to be moved without having to start the engine. In this way, power consumption is lowered and total efficiency of the mower is increased.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/645,111 filed May 10, 2012, which is hereby incorporated herein byreference.

FIELD OF INVENTION

The present invention relates generally to transmissions, and moreparticularly to transmissions for use in vehicles, such as mowingmachines.

BACKGROUND

Hydrostatic transmissions have many uses, including the propelling ofvehicles, such as mowing machines. A typical hydrostatic transmissionsystem includes a variable displacement hydraulic pump connected in aclosed hydraulic circuit with a fixed or variable displacement hydraulicmotor. The closed hydraulic circuit includes a first conduit connectingthe main pump outlet with the motor inlet and a second conduitconnecting the motor outlet with a pump inlet. Either of these conduitsmay be the high pressure line depending upon the direction of pumpdisplacement from neutral. For most applications, the pump is driven bya prime mover, such as an internal combustion engine or an electricalmotor, at a certain speed in a certain direction. Changing thedisplacement of the main pump will change its output flow rate, whichcontrols the speed of the motor. Pump outflow can be reversed, thusreversing the direction of the motor. In a vehicle, the motor is oftenconnected through suitable gearing to the vehicle's wheels or tracks.

In some vehicles, such as zero-turn-radius mowers, separate hydraulicpumps and motors are used to independently drive separate wheels of anaxle. By independently driving the wheels in opposite directions, forexample, the vehicle can be made to turn with zero radius.Zero-turn-radius mowers are increasingly popular as the size and costsof such mowers decrease. As the size of such mowers decreases, however,the space available for the hydraulic components and/or the prime moveralso decreases.

SUMMARY OF INVENTION

The present invention provides an electro-hydraulic drive systemincluding first and second electro-hydraulic transmissions for drivingrespective wheels, the transmissions each including an electric motor, ahydraulic pump driven by the electric motor, and a hydraulic motor driveby the hydraulic pump. When used in a turf vehicle, such as azero-turn-radius mower, the electro-hydraulic drive system operates thewheels independently from an engine of the mower, thereby allowing themower to be moved without having to start the engine. In this way, powerconsumption is lowered and total efficiency of the mower is increased.

According to an aspect of the invention, an electro-hydraulic drivesystem is provided that includes a first electro-hydraulic transmissionfor driving a first wheel, the first electro-hydraulic transmissionincluding a first electric motor, a first hydraulic pump coupled to anddriven by the first electric motor, and a first hydraulic motor coupledto and driven by the first hydraulic pump, the hydraulic motor includingan output shaft for driving the wheel, and a second electro-hydraulictransmission for driving a second wheel, the second electro-hydraulictransmission including a second electric motor, a second hydraulic pumpcoupled to and driven by the second electric motor, and a secondhydraulic motor coupled to and driven by the second hydraulic pump, thehydraulic motor including an output shaft for driving the wheel.

In an embodiment, the apparatus further includes at least one controllercoupled to the first and second electric motors for controlling thefirst and second electric motors.

In another embodiment, the apparatus further includes a storage devicecoupled to the controller, wherein the storage device is configured topower the first and second electric motors.

In still another embodiment, the storage device includes at least onebattery and/or capacitor.

In yet another embodiment, the first and second hydraulic pumps aregerotor pumps.

In a further embodiment, the first and second hydraulic motors aregerotor motors.

In another embodiment, the first and second electro-hydraulictransmissions additionally include first and second reservoirsrespectively for fluid to flow to/from the respective hydraulic pump.

In still another embodiment, the first and second electro-hydraulictransmissions additionally include first and second pump plates thathouse the first and second hydraulic pumps respectively.

In yet another embodiment, the first and second electro-hydraulictransmissions additionally include first and second porting plates, eachporting plate having a pump mount surface coupled to the respective pumpplate and a motor mount surface coupled to an end port plate of therespective hydraulic motor, wherein the porting plates include first andsecond fluid passages for directing hydraulic fluid between thehydraulic pumps and hydraulic motors.

In a further embodiment, the pump mount surface of the porting plateincludes a path for allowing hydraulic fluid to flow to/from a cavity inthe pump mount surface below the hydraulic pump from/to a reservoir.

In another embodiment, the first and second electro-hydraulictransmissions additionally include first and second valve plates coupledto the first and second pump plates respectively on sides of the pumpplates opposite the porting plates, wherein the valve plates houserespective bypass valves for bypassing the electro-hydraulic drivesystem.

In still another embodiment, the first and second electric motorsinclude respective output shafts that directly drive the first andsecond hydraulic pumps respectively.

In a further embodiment, the first and second electric motors includefirst and second output shafts respectively, and the first and secondhydraulic pumps include first and second input shafts respectively,wherein the first and second output shafts are respectively coupled tothe first and second input shafts for driving the respective hydraulicpumps.

According to another aspect of the invention, a mower is provided thatincludes a frame, a mower deck supported by the frame, an engine mountedto the frame and configured to power the mower deck, anelectro-hydraulic drive system including a first electro-hydraulictransmission for driving a first wheel, the first electro-hydraulictransmission including a first electric motor, a first hydraulic pumpcoupled to and driven by the first electric motor, and a first hydraulicmotor coupled to and driven by the first hydraulic pump, the hydraulicmotor including an output shaft for driving the wheel and a secondelectro-hydraulic transmission for driving a second wheel, the secondelectro-hydraulic transmission including a second electric motor, asecond hydraulic pump coupled to and driven by the second electricmotor, and a second hydraulic motor coupled to and driven by the secondhydraulic pump, the hydraulic motor including an output shaft fordriving the wheel and a controller coupled to the first and secondelectric motors for controlling the first and second motors.

In an embodiment, the storage device is coupled to the controller,wherein the storage device is configured to power the first and secondelectric motors.

In another embodiment, the mower further includes a generator coupled tothe controller and an output shaft of the engine, the generator beingconfigured to charge the storage device.

In still another embodiment, the electro-hydraulic drive system operatesindependently from the engine.

In yet another embodiment, the controller is configured to receiveinputs from wheel speed sensors, engine rpm, deck spindle speed, handlever position, engine load, and/or battery/motor current draw to adjustcontrol of the first and second electric motors.

According to another aspect of the invention, an integratedelectro-hydraulic transmission for driving a wheel in a turf vehicle isprovided, the transmission including an electric motor, a gerotor pumpcoupled to and driven by the electric motor, and a gerotor motor coupledto and driven by the gerotor pump, the gerotor motor including an outputshaft for driving the wheel.

In an embodiment, the electric motor includes an output shaft thatdirectly drives the gerotor pump.

In another embodiment, a second integrated electro-hydraulictransmission is provided, wherein the second integratedelectro-hydraulic transmission includes an electric motor, a gerotorpump coupled to and driven by the electric motor, and a gerotor motorcoupled to and driven by the gerotor pump, the gerotor motor includingan output shaft for driving a second wheel.

The foregoing and other features of the invention are hereinafterdescribed in greater detail with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an exemplary zero-turn-radius moweremploying a hydro-electric transmission to which the principles of theinvention can be applied, as discussed below.

FIG. 2 is a schematic view of the zero-turn-radius mower.

FIG. 3 is a perspective view of an exemplary left hand electro-hydraulicdrive assembly.

FIG. 4 is a top view of the left hand electro-hydraulic drive assembly.

FIG. 5 is a front view of the left hand electro-hydraulic driveassembly.

FIG. 6 is a left side view of the left hand electro-hydraulic driveassembly.

FIG. 7 is a cross-sectional view of the left hand electro-hydraulicdrive assembly taken about line A-A in FIG. 6.

FIG. 8 is an enlarged view of section B-B in FIG. 7.

FIG. 9 is a top view of a hydraulic motor and porting plate.

FIG. 10 is a side cross-sectional view of the porting plate and aportion of the hydraulic motor.

FIG. 11 is a perspective view of an exemplary right handelectro-hydraulic drive assembly.

FIG. 12 is a top view of the right hand electro-hydraulic driveassembly.

FIG. 13 is a front view of the right hand electro-hydraulic driveassembly.

FIG. 14 is a right side view of the right hand electro-hydraulic driveassembly.

FIG. 15 is a cross-sectional view of the left hand electro-hydraulicdrive assembly taken about line A-A in FIG. 14.

FIG. 16 is an enlarged view of section B-B in FIG. 15.

FIG. 17 is a perspective view of another exemplary left handelectro-hydraulic drive assembly.

FIG. 18 is a top view of the left hand electro-hydraulic drive assembly.

FIG. 19 is a front view of the left hand electro-hydraulic driveassembly.

FIG. 20 is a left side view of the left hand electro-hydraulic driveassembly.

FIG. 21 is a cross-sectional view of the left hand electro-hydraulicdrive assembly taken about line A-A in FIG. 20.

FIG. 22 is an enlarged view of section B-B in FIG. 21.

FIG. 23 is a cross-sectional view of the left hand electro-hydraulicdrive assembly taken about line C-C in FIG. 20.

DETAILED DESCRIPTION

The principles of the present invention have particular application tomowers, such as zero-turn-radius mowers, and thus will be describedbelow chiefly in this context. It will, of course, be appreciated andalso understood that the principles of the application may be useful inother vehicles, such as vehicles utilizing mechanical, hydrostatic,hydraulic, or electric drive systems.

Referring now to the drawings in detail, and initially to FIG. 1, anexemplary zero-turn-radius mower 10 is illustrated. The mower 10includes a frame 12, a mower deck 14 supported by the frame 12 formowing grass, an operator seat 16, and a plurality of controls 18 foroperating the mower 10. A rear mounted engine 30 (FIG. 2) mounted to theframe 12 behind the seat 16 provides power to the mower deck 14 and/orattachments. The engine 30 may be any suitable engine, such as agasoline engine, a diesel engine, a propane engine, etc. that drives abelt or power take-off connected to the mower deck 14 and/orattachments. The engine may be a relatively small engine, such as a10-15 horsepower engine. The design of the illustrated mower 10 ismerely exemplary in nature, and it will be appreciated that other mowerdesigns and vehicle types can be used in accordance with the invention.

Turning now to FIG. 2, a schematic view of the mower 10 is shown. Theexemplary mower 10 includes an electro-hydraulic drive system 40, whichis a hybrid drive system for vehicles utilizing mechanical, hydrostatic,hydraulic, or electric drive systems. The engine 30 powers the mowerdeck 14 and/or attachments, while first and second electro-hydraulictransmissions 50 and 52 of the electro-hydraulic drive system 40 arecontrolled independently from the engine 30 by a controller 70 to driverespective rear wheels 20 and 22 to propel the mower 10 and providezero-turn-radius functionality.

The first electro-hydraulic transmission 50 includes a first electricmotor 54, a first hydraulic pump 56 coupled to and driven by the firstelectric motor 54, and a first hydraulic motor 58 coupled to and drivenby the first hydraulic pump 56. Similarly, the second electro-hydraulictransmission 52 includes a second electric motor 60, a second hydraulicpump 62 coupled to and driven by the second electric motor 60, and asecond hydraulic motor 64 coupled to and driven by the second hydraulicpump 62.

The first and second electric motors 54 and 60 may be any suitableelectric motor, such as high voltage brushless DC motor, for example a48v motor. The first and second hydraulic pumps 56 and 62 may be anysuitable pump, such as a gerotor pump, for example a small displacement4.5cc gerotor pump. The first and second hydraulic motors 58 and 64 maybe any suitable motor, such as a low speed/high torque gerotor motor,for example a 260cc gerotor motor. The first and second hydraulic motors58 and 64 include first and second output shafts 66 and 68,respectively, that may be coupled to an axle shaft or that may serve asthe axle shaft for driving the respective wheels 20 and 22. The firstand second hydraulic motors are also provided with attachment lugs 67(FIG. 3) having through holes for receiving fasteners for mounting thehydraulic motors 66 and 68, and thereby the first and secondelectro-hydraulic transmissions 50 and 52, to the mower 50.

Coupled to the first and second electric motors 54 and 60 is thecontroller 70, which may be coupled to the motors in any suitablemanner, such as by suitable conductors 72 and 74. The controller 70 isconfigured to receive inputs from wheel speed sensors, engine rpm, deckspindle speed, hand lever position, engine load, battery/motor currentdraw, etc. Based on the inputs, the controller 70 can command theelectro-hydraulic system 40 to operate and react to provide for highsystem efficiency during operation, and the inputs may additionally beused by programs in software in the controller to increase control,safety, and system life.

For example, the controller 70 may provide increased efficiency byallowing the engine to be revolution matched to a prevailing turfcondition, such as by reducing/increasing the engine speed based on tipspeed of mower blades. For example, mowing light grass at a slow pacerequires less energy to the mowing deck/blades than mowing heavy grass,and therefore the controller 70 is configured to alter the engine speedto conserve energy. The controller 70 may also be configured to limitwheel speed/torque automatically to prevent skidding and/or turf diggingduring turns. The controller 70 may additionally be configured toprovide an auto tracking feature to keep the mower moving straightduring a long stretch of turf. The controller 70 may further beconfigured to allow for different driving styles, such as aggressive orcompliant driving styles, to be available via a button or switch on themower 10 to add scalable performance and tuneability.

The controller 70 is also coupled to a power storage device 76, such asa battery, plurality of batteries, capacitor, plurality of capacitors orcombination thereof, in any suitable manner, such as by suitableconductors 78 to provide power to the first and second electro-hydraulicdrive assemblies 50 and 52. The storage device 76 allows theelectro-hydraulic drive system 40 to be run independently from theengine 30, thereby allowing the mower 10 to be driven, for example to bemoved on/off a trailer and to/from a mowing site, without running theengine 30.

The power storage device 76 may be charged in any suitable manner, suchas by a standard charging system when the mower 10 is not being used.Additionally or alternatively, the mower 10 may include analternator/generator 80 coupled to the controller 70 to charge the powerstorage device 76. The alternator/generator 80 may also be coupled to anoutput shaft of the engine 30 along with a clutch for a pulley/beltdrive 82. The alternator/generator 80 may be coupled to the controller70 in any suitable manner, such as by conductors 84. Thealternator/generator 80 may be provided to extend battery life or toallow for a battery-less system architecture. The alternator/generator80 and/or the standard charging system supply energy to the first andsecond electric motors 54 and 60 and/or the power storage device 76 viathe controller 70 and suitable software.

By using the electro-hydraulic drive system 40, the engine 30 does notneed to be started until it is desired to operate the mower deck 14,thereby lowering power consumption and increasing total efficiency ofthe mower 10. It will also be appreciated that because the engine 30does not power the electro- hydraulic drive system 40, parasitic lossesare avoided that result from, for example, running a hydraulic system,and specifically a hydraulic pump, at full speed while the mower is atrest or operating at a low speed. Moreover, by providing theelectro-hydraulic drive system 40 to power the wheels 20 and 22 and theengine 30 to power the mower deck 14 and/or attachments, the mower 10may be operated at longer run times at required torques withoutrequiring large motors and large controllers that add weight and take upspace in the mower.

Turning now to FIGS. 3-10, an embodiment of the first electro-hydraulicdrive assembly 50 is shown. The first electro-hydraulic drive assembly50 is shown as a left hand electro-hydraulic drive assembly. FIGS. 11-16show an embodiment of the second electro-hydraulic drive assembly 52,which is shown as a right hand assembly. It will be appreciated that theright hand assembly is substantially the same as the left hand assembly,and thus will not be described in detail.

As noted above, the first electro-hydraulic drive assembly 50 includesthe first electric motor 54, the first hydraulic pump 56, and the firsthydraulic motor 58. The first electro-hydraulic drive assembly 50 alsoincludes a reservoir 100 having a lid 101 and breather 103, a casing102, a valve plate 104, a pump plate 106, and a porting plate 108. Oneor more bolts 110 extends through bolt holes in a plate 112 coupled toor integrally formed with the casing 102, the valve plate 104, the pumpplate 106, and the porting plate 108 to couple the plates.

As best shown in FIG. 7, the casing 102 houses the electric motor 54 andincludes one or more openings 114 for allowing air to flow into and outof the casing 102. The casing 102 also houses is a fan 116 for coolingthe electric motor 54 and a coupler 118 that couples an output shaft 120of the electric motor 54 to a first end of an input shaft 122 thatdrives the hydraulic pump 56. The input shaft extends from the casing102 through the valve plate 104 and the pump plate 106, and a second endof the input shaft 122 is disposed in a cavity 124 in the porting plate108.

The valve plate 104 is disposed between the casing 102 and the pumpplate 106 and houses suitable valves for controlling hydraulic fluidflow to the hydraulic pump 56. The valve plate 104 also houses a bypassvalve 130 in a bypass chamber 132. The bypass valve 130 may be operatedto allow fluid to flow from the reservoir 100 to the hydraulic pump 56or to allow the hydraulic pump 56 and the hydraulic motor 58 to bebypassed, for example for the mower 10 to be towed. The bypass valve 130is sealed in the bypass chamber 132 by a suitable seal 131 and held inthe chamber 132 by a suitable retainer, such as snap ring 133. One ormore stops 135 may be provided for a lever 137 of the bypass valve 130to limit travel of the lever between the stops.

The pump plate 106 houses the hydraulic pump 56 and includes a sealgroove that receives a suitable seal 134, such as an o-ring, to seal atop surface of the pump plate 106 to a bottom surface of the valve plate104. Extending through the pump plate 106 is the second end of the inputshaft 122, which extends into the cavity 124 in the porting plate 108. Aportion of the input shaft 122 proximate the second end meshes with aninner rotor 136 of the hydraulic pump 56, which is surrounded by anouter rotor 138. Rotation of the input shaft 122 causes the inner rotor136 to move, thereby pumping fluid to the hydraulic motor 58. The inputshaft 122 is surrounded by first and second needle bearings 137 and 139,and sealed between the valve plate 104 and casing 102 by a seal 141. Thefirst needle bearing 137 surrounds the input shaft 122 in the valveplate 104 and the second needle bearing 139 surrounds the input shaft122 in the cavity 124 of the porting plate 108.

As shown in FIG. 9, the porting plate 108 includes a pump mount surface140 that abuts a bottom surface on the pump plate 106. The pump mountsurface 140 includes a seal groove 142 that receives a suitable seal144, such as an o-ring, for sealing between the pump plate 106 and theporting plate 108. As shown in FIG. 10, the porting plate 108 alsoincludes a motor mount surface 146 that abuts and is coupled to an endport plate 148 of the hydraulic motor 58. The porting plate 108 iscoupled to the end port plate 148 in any suitable manner, such as bybolts 150 that extend through the motor mount surface 146 and the endport plate 148 into the motor 58.

The pump mount surface includes ports 152 and 154 for communicating withthe hydraulic pump 56. The motor mount surface 146 includes ports 156and 158 (not shown) for communicating with the hydraulic motor 58, andspecifically for communicating with ports in the end port plate 148 thatdirect fluid into the hydraulic motor to rotate the output shaft 66 ofthe hydraulic motor 58. Connecting the ports 152 and 154 in the pumpmount surface 140 and the ports 156 and 158 in the motor mount surface146 are first and second fluid flow passages 162 and 164, which areconfigured to direct the hydraulic fluid between the hydraulic pump 56and hydraulic motor 58. The passages 162 and 164 in the porting plate108 may be formed in any suitable manner, such as by drilling throughthe plate, and portions of one or more of the passages may be plugged bya suitable plug, such as plug 166.

Referring again to FIGS. 7 and 9, fluid may flow to the reservoir 100from the cavity 124 to provide a bleed passage for fluid trapped belowthe needle bearing 139, and fluid may flow from the reservoir 100 intothe cavity 124 below the needle bearing 139 as needed. To accomplish theforegoing, hydraulic fluid can flow to/from the reservoir 100 through apassage 170 at a bottom of the reservoir 100 and into the bypass chamber132. The fluid can flow through the chamber 132 and around flats 172 onthe bypass valve 130 to a passage 174 at the bottom of the valve plate104. The fluid then flows through a passage 176 extending through thepump plate 106 to a passage 178 in the porting plate 108, and then tothe cavity 124 in the porting plate 108. The passage 178 is a serpentinepassage that extends from an area in between the seal groove 142 and theport 154 to the cavity 124 in the porting plate 108 between the ports152 and 154.

Turning now to FIGS. 17-23, an exemplary embodiment of the firstelectro-hydraulic drive assembly is shown at 250. The firstelectro-hydraulic drive assembly 250 is substantially the same as theabove-referenced first electro-hydraulic drive assembly 50, andconsequently the same reference numerals but indexed by 200 are used todenote structures corresponding to similar structures in the firstelectro-hydraulic drive assembly. In addition, the foregoing descriptionof the first electro-hydraulic drive assembly 50 is equally applicableto the first electro-hydraulic drive assembly 250 except as noted below.Moreover, it will be appreciated upon reading and understanding thespecification that aspects of the electro-hydraulic assemblies may besubstituted for one another or used in conjunction with one anotherwhere applicable.

Referring to FIG. 21, the electro-hydraulic drive assembly 250 includesthe first electric motor 254, the first hydraulic pump 256, and thefirst hydraulic motor 258. The electric motor 254 is enclosed in a motorcasing 380 and is bolted to the valve plate 304. The electric motorincludes an output shaft 320 that extends through the valve plate 304and the pump plate 306 to mesh with a rotor 336 of the hydraulic pump256 to directly drive the hydraulic pump 256.

Referring to FIG. 23, the valve plate 304 includes a plurality ofsuitable valves for controlling hydraulic fluid flow to the hydraulicpump 256, such as check valves 382 and 384. The valves are disposed inrespective valve chambers 386 and 388, which communicate with the bypasschamber 332 and passages 390 and 392. Portions of the passages 390 and392 may be plugged by a suitable plug, such as plug 394.

Although the invention has been shown and described with respect to acertain embodiment or embodiments, it is obvious that equivalentalterations and modifications will occur to others skilled in the artupon the reading and understanding of this specification and the annexeddrawings. In particular regard to the various functions performed by theabove described elements (components, assemblies, devices, compositions,etc.), the terms (including a reference to a “means”) used to describesuch elements are intended to correspond, unless otherwise indicated, toany element which performs the specified function of the describedelement (i.e., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure which performs thefunction in the herein illustrated exemplary embodiment or embodimentsof the invention. In addition, while a particular feature of theinvention may have been described above with respect to only one or moreof several illustrated embodiments, such feature may be combined withone or more other features of the other embodiments, as may be desiredand advantageous for any given or particular application.

What is claimed is:
 1. An electro-hydraulic drive system including: afirst electro-hydraulic transmission for driving a first wheel, thefirst electro-hydraulic transmission including a first electric motor, afirst hydraulic pump coupled to and driven by the first electric motor,and a first hydraulic motor coupled to and driven by the first hydraulicpump, the hydraulic motor including an output shaft for driving thewheel; and a second electro-hydraulic transmission for driving a secondwheel, the second electro-hydraulic transmission including a secondelectric motor, a second hydraulic pump coupled to and driven by thesecond electric motor, and a second hydraulic motor coupled to anddriven by the second hydraulic pump, the hydraulic motor including anoutput shaft for driving the wheel.
 2. The electro-hydraulic apparatusaccording to claim 1, further including at least one controller coupledto the first and second electric motors for controlling the first andsecond electric motors.
 3. The electro-hydraulic drive system accordingto claim 2, further including a storage device coupled to thecontroller, wherein the storage device is configured to power the firstand second electric motors.
 4. The electro-hydraulic drive systemaccording to claim 3, wherein the storage device includes at least onebattery and/or capacitor.
 5. The electro-hydraulic drive systemaccording to claim 1, wherein the first and second hydraulic pumps aregerotor pumps.
 6. The electro-hydraulic drive system according to claim1, wherein the first and second hydraulic motors are gerotor motors. 7.The electro-hydraulic drive system according to claim 1, wherein thefirst and second electro-hydraulic transmissions additionally includefirst and second reservoirs respectively for fluid to flow to/from therespective hydraulic pump.
 8. The electro-hydraulic drive systemaccording to claim 1, wherein the first and second electro-hydraulictransmissions additionally include first and second pump platesrespectively that house the first and second hydraulic pumpsrespectively.
 9. The electro-hydraulic drive system according to claim8, wherein the first and second electro-hydraulic transmissionsadditionally include first and second porting plates respectively, eachporting plate having a pump mount surface coupled to the respective pumpplate and a motor mount surface coupled to an end port plate of therespective hydraulic motor, wherein the porting plates include first andsecond fluid passages for directing hydraulic fluid between thehydraulic pumps and hydraulic motors.
 10. The electro-hydraulic drivesystem according to claim 9, wherein the pump mount surface of eachporting plate includes a path for allowing hydraulic fluid to flowto/from a cavity in the pump mount surface below the hydraulic pumpfrom/to a reservoir.
 11. The electro-hydraulic drive system according toclaim 9, wherein the first and second electro-hydraulic transmissionsadditionally include first and second valve plates coupled to the firstand second pump plates respectively on sides of the pump plates oppositethe porting plates, wherein the valve plates house respective bypassvalves for bypassing the electro-hydraulic drive system.
 12. Theelectro-hydraulic drive system according to claim 1, wherein the firstand second electric motors include first and second output shaftsrespectively, and the first and second hydraulic pumps include first andsecond input shafts respectively, wherein the first and second outputshafts are respectively coupled to the first and second input shafts fordriving the respective hydraulic pumps.
 13. The electro-hydraulic drivesystem according to claim 12, wherein the first and secondelectro-hydraulic transmissions additionally include first and secondcouplers respectively that couple the first and second input shafts tothe first and second output shafts respectively.
 14. A mower including:a frame; a mower deck supported by the frame; an engine mounted to theframe and configured to power the mower deck; an electro-hydraulic drivesystem including: a first electro-hydraulic transmission for driving afirst wheel, the first electro-hydraulic transmission including a firstelectric motor, a first hydraulic pump coupled to and driven by thefirst electric motor, and a first hydraulic motor coupled to and drivenby the first hydraulic pump, the hydraulic motor including an outputshaft for driving the wheel; and a second electro-hydraulic transmissionfor driving a second wheel, the second electro-hydraulic transmissionincluding a second electric motor, a second hydraulic pump coupled toand driven by the second electric motor, and a second hydraulic motorcoupled to and driven by the second hydraulic pump, the hydraulic motorincluding an output shaft for driving the wheel; and a controllercoupled to the first and second electric motors for controlling thefirst and second motors.
 15. The mower according to claim 14, furtherincluding a storage device coupled to the controller, wherein thestorage device is configured to power the first and second electricmotors.
 16. The mower according to claim 15, wherein theelectro-hydraulic drive system operates independently from the engine.17. The mower according to claim 15, further including a generatorcoupled to the controller and an output shaft of the engine, thegenerator being configured to charge the storage device.
 18. Anintegrated electro-hydraulic transmission for driving a wheel in a turfvehicle, the transmission including: an electric motor; a gerotor pumpcoupled to and driven by the electric motor; and a gerotor motor coupledto and driven by the gerotor pump, the gerotor motor including an outputshaft for driving the wheel.
 19. The integrated electro-hydraulictransmission of claim 18 in combination with a second integratedelectro-hydraulic transmission, wherein the second integratedelectro-hydraulic transmission includes an electric motor, a gerotorpump coupled to and driven by the electric motor, and a gerotor motorcoupled to and driven by the gerotor pump, the gerotor motor includingan output shaft for driving a second wheel.
 20. The combinationaccording to claim 19, wherein the first and second electro-hydraulictransmissions additionally include first and second couplersrespectively that couple a shaft of the respective electric motor to ashaft of the respective gerotor pump.